Here is my attempt at the outward leg for you all to review. It uses NCN 65 in various places where it makes sense to, and elsewhere the quietest roads that don't involve major detours
Here's a rough map (and elevation profile):
Description:
York railway station, NCN 65/TPT from the racecourse to Moor Ln, Deighton, Escrick, Skipwith, South Duffield, Hemingbrough, NCN 65/TPT, Barmby on the Marsh, Asselby, Howden, Kilpin, Laxton, Yokefleet, Faxfleet, NCN 65/TPT, Broomfleet, Ellerker, then criss-crossing the A63 through Elloughton and Melton to North Ferriby, Hessle, Humber Bridge, Waters Edge Country Park visitor centre cafe in Barton-upon-Humber
Distance approximately 80 km (50 miles).
I apologise for the extreme lumpiness of the route. I tried to keep the climbing down as much as possible, but couldn't avoid a few metres (feet) here and there ... Opinions please!
I've attached a gpx file for this proposed outward leg.